This invention relates to a method of producing a lithographic plate precursor which is imageable by direct heat and processable with water.
Currently the commonest method of preparing a lithographic plate is to image a photosensitive lithographic plate to UV light and to prepare the plate therefrom using an aqueous developing solution.
The differentiation between image and non-image areas is made in the exposure process. In conventional lithography a film original is applied to the plate with a vacuum to ensure good contact and the plate is then blanket exposed to a light source, a portion of which is composed of UV radiation.
More recent developments in the field of lithographic printing plates have provided imaging devices which allow for the preparation of direct digitally written printing forms. In the commonest method digital imaging information is used to image the plate directly by laser radiation without the need to utilise an imaging master such as a photographic transparency. The fastest growing trend is to utilise lasers which emit infra-red radiation. Such imaging systems are, however, costly due to the lasers required and this is a contributing factor to the slow rate of uptake of this new imaging technology within the print industry. However, imaging devices are now available commercially which can image media using direct heat via means of a heated stylus or nib controlled by an image stored in a computer. Such devices are much cheaper than the equivalent laser imagers and are reducing the entry cost for direct plate imaging systems. Following the exposure the differentiation is revealed during the development step. For typical negative acting systems this involves washing away material from the plate which was not imaged by the exposing source with the aid of a developing solution which may be highly alkaline, e.g. pH of 13, and based on an organic solvent. When aqueous developing solutions comprising volatile organic solvents or which are strongly alkaline in nature are used, their use and disposal presents an environmental problem.